On 20 April 2011, photojournalists Tim Hetherington and Chris Hondros were killed when they came under attack in Misrata, Libya. While it was previously thought they were the collateral victims of a rocket-propelled attack from nearby, US Marine Corps officer Chris Chivers later discovered the attack was launched from further away and had been called in by a spotter working for Muammar Gaddafi's forces. Last month, a UK court ruled their deaths to be unlawful.

South African photojournalist Anton Hammerl was also shot by pro-Gaddafi forces in April 2011 and left for dead in the Libyan desert, where he is believed to have succumbed to his wounds. His body has never been recovered.

On 22 February 2012, The Sunday Times correspondent Marie Colvin and freelance photographer Rémi Ochlik were murdered when their press centre in Homs, Syria, was targeted by the Syrian regime. To date, no one has been prosecuted for their deaths.

Now, a year later, a group of journalists, editors, photographers and legal experts have launched an international campaign to "draw sharper attention to the growing number of journalists who have been killed and injured in armed conflict, in some cases as a result of direct targeting by the belligerents; to develop a public diplomacy, institutional and legal agenda to combat this more effectively; and to investigate and collect evidence in support of prosecutable cases in this area".

The campaign, dubbed A Day Without News?, originated during a panel discussion at the United Nations headquarters in New York. "Aidan Sullivan, Michael Kamber, Stephen Mayes and I were speaking on a panel together at the United Nations last year, and a lot of the discussion ended up being about journalists and the risks they take when covering conflicts," says photographer Lynsey Addario.

During the discussion, Sullivan, who leads Reportage by Getty Images, asked the panel whether there was "a better way to legally protect journalists and make the world aware of the critical importance to do so. Despite the fact that it is officially a war crime to target journalists, there has been little respect for, or enforcement of, international human rights laws when applied to journalists. And it doesn't seem that the public recognises the risk in governments failing to do so," write the campaign's founders.

The campaign has been initiated by Sullivan, with the help of Vanity Fair's David Friend, photographers Addario, Tom Stoddart, John Moore, Sir Daniel Bethlehem QC and Sara Solfanelli. The goal of A Day Without News? is to generate grassroots support within the journalistic community in an effort to further the work of the Committee to Protect Journalists, Reporters Without Borders and Human Rights Watch, among other organisations. "We're working closely with these organisations, and they've all been really helpful," Sullivan tells BJP. "We're not trying to take anything away from them; on the contrary, what we're doing is supporting them. They are the professionals. It's their day job."

The campaign will work to serve these organisations' missions, "hopefully by building public support through publicity, increasing pressure for change through diplomacy, and facilitating the identification, investigation and prosecution of war crimes committed against journalists".

To do so, the campaign is looking to partner with third-party organisations such as Columbia Law School or Columbia Journalism School to create a clinic whose goal would be to investigate war crimes, "including Rémi's and Marie's death", which could be prosecuted, says Sullivan. "That is the hardest part because finding real evidence of a war crime is not always easy."

For Addario, a photographer who was kidnapped twice - once in Falluja, Iraq in 2004, and more recently in Libya in March 2011 - such a campaign is necessary, "especially now that journalists are being deliberately targeted", she tells BJP. "We need to bring that discussion to the table, and we need to have governments recognise the consequences of killing journalists. Someone has to be held responsible."

It is ambitious, she admits, but "I remember in Libya, when we were kidnapped, they had us face down on the ground with their guns to our heads. They were deciding whether or not to execute us. Someone said: ‘You can't shoot them, they're Americans.' They were aware of the repercussions for killing Americans. We were in the middle of the desert; they could have killed us and left us in a mass grave and no one would have been responsible. But someone actually paused to say that since we were Americans, they couldn't just kill us. That sentence needs to evolve to: ‘We can't kill them, they are journalists.' That's where we need to get to with this dialogue."

The campaign has also received the support of Ochlik's and Colvin's families. "It's important to show the world not as we imagine it but as it is: beautiful, amazing but so, so vicious," says Emilie Blachère, Ochlik's girlfriend.

"And photographers and journalists do this every day, every hour. Some die for this. We have to make the general public sensitive to the importance of the press.

"One year ago, on 22 February, Rémi died in Syria doing his job, and because he was doing his job, he was targeted, and still nobody has been arrested. The murder of journalists and photographers carries on with impunity.

"Rémi's family and I are really touched by the A Day Without News? campaign. We support this project because we want reporters to go everywhere, but we need them to come back safe and sound to continue their work."

Cat Colvin, Marie Colvin's sister, adds: "My family is so deeply appreciative of the efforts of Aidan Sullivan and the A Day Without News? campaign, not only for raising awareness of my sister's murder at the hands of the Syrian government, but also of the growing numbers of journalists and photographers who are targeted in war zones every day."

The campaign's organisers are now calling on the public to help spread the word. "Over the course of the next 12 months, we will continue to meet with multiple governments that have shown interest and support for the campaign, to push policy and diplomacy to fight against impunity, investigate and ultimately prosecute cases where journalists and media personnel have been targeted and killed."

A Day Without News? comes as the industry is debating whether freelance photographers should report from conflict zones and whether they should receive the support of media organisations that buy their work. Last month, The Sunday Times reportedly told its freelance photographers that it would not accept any work from Syria due to security reasons. "I don't think photographers should be banned from covering wars, because we are the objective people on the ground and we understand the ethics of journalism," says Addario. "Citizen journalism is very important, of course, especially in places such as Syria, where there are few journalists covering it. But we don't know their biases so, when we look at their footage, we can't always confirm what we're seeing. It's very important that journalists continue to cover war zones, and news organisations have to make sure that when they send someone in they have their backs, they have insurance and they can set the wheels in motion if something happens to them."

She adds: "They have to stand behind whoever they send in. Right now in Syria, you have dozens of 20 year olds who are in their first year of covering war - and they are in there without any backing from any publications. I think it's very brave of them, and I appreciate any coverage from anyone. But the publications that are buying from these freelancers need to step up and pay for their insurance and make sure they have the gear they need. They need to help them."

The campaign has received the support of journalists and photographers such as Don McCullin, Christiane Amanpour, James Nachtwey, Patrick Chauvel, Sebastian Junger and Yuri Kozyrev among many others.

For more information and to support the campaign, visit www.adaywithoutnews.com.

UPDATE: A Day Without News has also received the support of UN Secretary General, Ban Ki-moon. "Every journalist killed is a vital voice lost," he says in a video message posted today. "Every murder represents a day without news, a day when society as a whole is weakened. This is why the UN Plan of Action on the Safety of Journalists and the Issue of Impunity is so important. Our goal is simple: to ensure that every journalist can do her or his job safely. Each year on World Press Freedom Day, May 3rd, we speak out for the safety of journalists, and for combating impunity, in the real and digital worlds. I welcome this opportunity to raise the flag in support of 'A Day without News'."